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COURSE CODE: APH505

COURSE TITLE: Animal Products and By-Products

NUMBER OF UNITS: 3 Units

COURSE DURATION: Three hours per week

COURSE DETAILS:

Course Coordinator: Dr. (Mrs.) K. A. Sanwo Email: [email protected] Office Location: COLANIM Building Other Lecturers: Prof. S. S. Abiola, Dr. O. M. Sogunle, Dr. L. T. Egbeyale

and Dr. O. S. Akinola

Pre- slaughter handling of different farm animals. Slaughtering methods, dressing and post-

mortem changes in meat. Meat quality. Methods of meat preservation. Processing of abattoir

by-products. Meat inspection and grading. Meat processing – bacon, sausages etc. Meat

hygiene. Milk products and processing e. g. ice – cream, butter, yoghurt, cheese etc. Egg

quality, handling, storage and grading. Animal by-products, blood, hooves faeces and their

uses. Hides and skin processing- flaying, curing, tanning. Hides and skin utilization.

This is a compulsory course for all 500 level students in the College of Animal Science and

Livestock Production. Students are expected to participate in all the course activities and have

minimum of 75% attendance of lectures and practical work to be able to write the semester

examination.

COURSE DETAILS:

COURSE CONTENT:

COURSE REQUIREMENTS:


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1. Dairy Cattle Husbandry, 2008. Agromisa Foundation and CTA, Wagenigen

2. Animal Products, Processing & Handling in the tropics, 2000 by Aduku & Olukosi

3. Meat Science and Technology: A Comprehensive Approach by Ikeme, A. I. African FEP Publishers Limited.

4. The Science of Meat and Meat Products by Price, J. F. and Schweigert, B. S. W.H. Freeman and Coy, San Fransisco.

5. The Principle of Meat Science by Forrest et al. W.H. Freeman and Coy, San Fransisco.

E

MEAT QUALITY AND MEAT PRESERVATION

Meat Quality

In recent years, meat quality has assumed a greater consumer significance and public attention

there is growing awareness of the link between diet and health and this is reflected in the demand

for more information and for products which are healthy and of consistently high quality. As a

consequence, this has lead to the demand for meat with a high lean content. On the other hand as

animals, and especially pigs and poultry, have become leaner, more complaints have been received

that the eating quality of the meat has declined, with complaints of dryness, toughness and lack of

taste and flavour. Other concerns are about food safety and hygiene, especially the presence of

micro-organisms, bacterial contamination and residues, as well as the welfare and husbandry

conditions under which animals are kept. Thus, both the diets fed to the animals and the systems of

animal production are being increasingly questioned. It is fortuitous that with the elucidation of the

major factors influencing meat quality and hygiene new opportunities are being created for the

development of a consistent, healthy, safe and attractive product which offers value for money.

Factors contributing to the eating quality of meat are:

1. Appearance

2. flavour (smell at abattoir, taste)

3. tenderness (chew time)

4. texture

LECTURE NOTES

READING LIST:


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Appearance: This has to do with the colour of meat and its freshness. Colour is determined by the

concentration of myoglobin. In young animals there is little concentration of myoglobin, but greater

in older animals and the meat becomes darker.

Flavour: Flavour is the combined result of the taste and smells senses and, because it is a subjective

property, is difficult to evaluate. Each species has its own characteristic flavour. Chemical reactions

resulting in some 1,000 compounds during contribute to the individual meat’s flavour

Tenderness: the meat from the young animals is more tender that the meat from old animals. At

time of cooking a lot of connective tissues will become soft especially meat from the young animals.

Connective tissues are easily broken in meat of young animals than the older animals because they

do not easily disintegrate.

Texture: this has to do with the diameter of muscle fibre when muscles are associated with closely

packed diameter. It is called fine texture and it is usually of young animals. Course texture is

associated with wider diameter of muscle and it is usually meat of older animals.

Hofmann (1987) and Russo (1988) have broadly classified meat quality characteristics into four

main categories:

Organoleptic properties

Technological quality

Nutritive value

Hygienic characteristics or food safety aspects

Organoleptic properties are the traits that influence the consumer to regularly purchase and eat

meat.

Technological qualities refer to the suitability of meat for further processing and are primarily

determined by treatment after slaughter.

Nutritional value is concerns with the chemical composition of the meat and its suitability for human

consumption.

Hygiene or safety implies freedom from harmful microorganisms and any residues.

These can be controlled through legislation, proper feeding designs and strategies, quality

management schemes on the farm and procedures in the slaughterhouse and processing plant.


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Components of Meat Quality

The main factors contributing to the eating quality of meat are tenderness, juiciness and colour.

These are dependent upon several metabolic and biological phenomena within the animal or carcass

and include the following:

Intramuscular content or marbling fat

Taint, especially the content of skatole, indole and testosterone

The type and fatty acid content of the animal’s diet and hence its carcass

Maturation or conditioning effects

Drip loss and maintenance of the integrity of the cell membrane post-mortem

Stress during transportation and lairage

The potential to flavour meat

The effect of feeding

Marbling fat

Acceptability in pigs, the effect of fat on eating quality depends on amount of marbling fat. Marbling

fat is the lipid found in the connective tissue surrounding the muscle fibre bundle. It has been

suggested that at least 2.0% marbling fat is required for optimal eating quality. Studies have shown

that the lower the back fat thickness, the lower the percentage of marbling fat and the less the

overall acceptability of the pork.

Taint and effect of skatole

Skatole (3-methyl indole) is a volatile compound produced in the hindgut of animal by microbial

degradation of the amino acid tryptophan. Majority of skatole is degraded in the liver and excreted

in the urine; the undegraded portion is deposited in the fat and muscle of the body. High

concentrations in these tissues give rise to unpleasant smell and taste of meat, especially in entire

male animals. Several studies have shown the effect of different diet component on skatole

concentration in the intestinal contents, as well as faeces and back fat of pig, e.g. fibre and CP

content.

Fatty and composition

In non-ruminants it is well established that simply changing the type and quantity of oil and fat in the

diet can change the fatty acid content of fat in the carcass. High concentration of polyunsaturated

fatty acids have been associated with low values for tenderness, juiciness, flavour and overall

acceptability; whereas high concentration of saturated and monounsaturated fatty acids resulted in


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high overall score. Also, there is an increased risk of rancidity and ‘off’ flavour when oils are used in

high quantity in pig diets.

Maturation and conditioning effects

The tenderness of meat improves with conditioning and storage after slaughter. Increasing the

conditioning period from 1 to 10 days at 1oC significantly improves the overall liking of meat. Also

the injection of calcium salt solutions, such as calcium chloride, into the carcass of animals have

been found to significantly improve the eating quality of meat and reduced the toughening effect of

cooking.

Oxidation stabilization and Drip loss

Lipids are important components of meat and enhance several desirable characteristic such as

flavour, tenderness and juiciness. However, one of the major causes of deterioration of meat, even

during cold storage, is lipid oxidation which ultimately results in unacceptable flavour, odours and

fatty acids, fat soluble vitamins and pigments. There is also concern about the production of

peroxides and aldehydes and the formation of ‘free radicals’ which produce harmful chemical

products.

Lipid oxidation is therefore a major cause of deterioration in the quality of meat. It also influences

the yield of saleable meat, since the disruption of the sub-cellular membrane destroys the integrity

of the cell wall, releasing intracellular fluid. This results in considerable fluid or drip loss, a major

problem and economic loss in both poultry and pork. It is therefore beneficial to reduce both the

occurrence and rate of lipid oxidation.

The role of vitamin E and Selenium as antioxidant is recognized and feeding of high dietary levels to

both pig and poultry has improved meat quality by reducing the rate of lipid oxidation and

maintaining the integrity of the cell membrane post-slaughter. This resulted in the meat keeping its

fresh appearance and colour for longer, as well as reduced drip loss, allowing better presentation of

both poultry and pork.

Stress

The most effective way to reduce the incidence of poor pork quality is to improve pre-slaughter

management and handling and thereby reduce stress. Stress both during transportation and pre-

slaughter can affect meat quality, since it can influence the rate and extent of post-mortem

acidification in the muscle. If stress is induced over a long period, then muscle glycogen is depleted

and dark, firm and dry (DFD) meat may result. Similarly, if the stress occurs immediately before or at

slaughter, then the rate glycolysis is increased at a time when carcass temperature is high, resulting

in PSE meat. Chromium has been recognized as an element which can assist animal to better


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tolerate stress, therefore reducing stress occurrence in animals, especially the organic form and

minimizing the incidence of both PSE and DFD-type meat.

Effects of Feeding

The supply of nutrients to animals, influence carcass composition since it directly affects growth rate

as well as the proportion of protein and fat in the body. The higher the level of feeding, the higher

the rate of lean and fat gain, therefore the higher the eating quality of the meat. it has also been

proved that the quality and type of raw ingredients included in the diets rather than the feeding

levels per-se was response for the effects.

Figure 1: Pale, Dark and normal meat

MEAT PRESERVATION

Meat gets putrefied due to the action of bacteria, moulds and yeasts. In an effort to get nourishment

from the meat after the meat alter the meat in various ways. To grow they require favourable

temperature. It is therefore customary to classify organisms according to their temperature

tolerance:

1. Psychrophiles which have an optimum temperature range of -2oC to 7oC.

2. Mesophiles which have an optimum temperature range of 10oC to 40oC

3. Thermophiles which have an optimum temperature range of 43oC to 66oC.

One can them preserve meat by reaching -2OC (sub optimal temp.) by chilling or freezing and 66OC

(super optimal temp.) by pasteurizing, cooking or sterilizing. Organisms also need water for growth

and so it is possible to preserve meat by dehydration, freezing or curing.


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Organisms cause spoilage by:

Disintegrating the connective tissue

Producing gases as hydrogen sulphide, carbon dioxide, ammonia etc.

Fermenting the muscle sugar (glycogen) to produce acetic and butyric acids, causing

offensive smell and tastes.

Discolouration of the meat by changing the myoglobin

Preservation by Cold

It is the simplest form of meat preservation. And it can be done for long time. This because bacteria

are unable to multiple at low temperature and due mainly to the fact that water is changed to ice.

1. Chilling meat: It is useful when meat will be preserved for only 35days. It loses very little in

appearance, nutritive value and taste. It is kept between -1.4oC and 1oC, preferably in the

dark as light has the effect of oxidizing fats. The atmosphere should be kept dry. A

concentration of 5% to 10% carbon dioxide helps to prevent the growth of mould and

bacteria. Meats under this condition require more space as they will need to be hung on

hooks to allow for adequate air circulation around them.

2. Freezing of meat: Temperature for ordinary freezing vary between -18OC and -5OC. This can

be kept for a long time. Frozen Beef can be stored for 12 months, veal slightly less, mutton

and lamb 8 months and pork 6 months without much deterioration. Frozen meat stored too

long become dry, less palatable and rancid. It is less durable after thawing than fresh killed

or chilled meat. Slow freezing or blast freezing can be used.

Preservation by Drying

Temperature, humidity and circulation of air are the key factors in drying of meat. Gradual

dehydration of meat cut to specific uniform shape that permits the equal and simultaneous drying of

whole batches of meat. The optimal conditions for a successful and easy drying of meat are:

Relative humidity of 30%

Warm and dry air

Small temperature difference between night and day.

Drying will be faster under high temperatures, low humidity and intensive air circulation. Relatively,

there is high water evaporation in the first day of drying, after which evaporation rate continually

decreases. As the meat dries it becomes smaller, thinner, thinner and to some degree wrinkled.

Consistency also changes from soft to firm and hard.


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Important Steps in Meat Drying:

i) slaughtering of the animal ii) carcass trimming iii) selection of the raw materials iv) proper cutting

and pre-treatment of the pieces v) proper arrangement of drying facilities vi) Influence of

unfavourable weather must be considered in order avoid quality problem or production losses

The secret of correct meat drying lies in maintaining a balance between water evaporation on the

meat surface and migration of water from the deeper layers. In other words, care must be taken

that meat surfaces do not become too dry while there is still high moisture content inside the meat

pieces. Dry surfaces inhibit the further evaporation of moisture, which may result in products not

uniformly dried and in microbiological spoilage starting from the areas where the moisture content

remains too high.

Selection of Meat for Drying

Lean meats without visible fat tissues adhering to muscle are suitable for drying.

Bovine meat, sheep, cameloids, goats and venison (e.g antilopes, dear etc.) are also used.

Meat from medium aged animal, in good condition and not fat.

Meat must be examined for undesirable alterations as discolouration, haemorrhagic spots,

off-flavour, manifestation of parasites etc. Such defects must be trimmed off.

Techniques of Cutting Meat Pieces for Drying

Cutting muscle into thin strips can be done in two ways:

Cutting after placing meat on clean chopping board (Fig 1)

Cutting the muscle in hanging position (Fig 2)

Pheripheral zone

Deeper meat layer


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In both cases the muscles have to be split exactly along the muscle fibres. The strips must be cut as

uniformly and as smoothly as possible and the diameter of the strip must remain the same

throughout the length. The length of the strips may differ, though it should not be less than 20 cm

and not more than 70 cm. Meat cut into shorter strips requires considerably more time for hooking

than the same quantity cut into longer strips. However, strips which are too long may break because

of their weight.

Figure 2: Cutting meat streeps from the muscle Figure 3: Cutting meat streeps from a on a chopping board. suspended muscle.

Recommended Treatment before Drying

Pre-salting: the use of a 14% salt solution is preferred. It is bactericidal in action and also protect

against insect during drying. The necessary amount of edible salt is added to water and dissolved by

intensive stirring, the meat strips are dipped into solution, soaked for about five minutes and then

drained. Draining can be done using plastic sieve. To make 14% of salt solution below are the

volumes of water to the weight of salt:

Water (l) Salt (g)

5 810

6 975

7 1140

10 1630


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Figure 4: Suspension of meat strips on hooks (A), loops (B), and by means of clips (C).

Figure 5: Sun meat dryer made of wood or metal (A and B)

Methods of suspending of meat strips for drying

Meat should be suspended individually from one end, thus ensuring, through arrangement on the

drying facility, free air circulation along the whole length of the pieces and fat and uniform drying.

The contact of meat pieces with each other must be avoided.


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The suspension of meat strips can be done in different ways (Figure 4):

Suspension using metal hooks

Suspension using loops

Suspension using metal clips

Installation for drying entire batches of meat

Sun meat dryer made of wood or metal

Mobile meat dryer

Meat dryer with protection against extreme influence e.g. roof type or normal with

protection.

Quality of the final products

Appearance: absence of large wrinkles and notches indicate uniform dehydration of meat

Colour: the surface and crosscut should be uniform and dark red.

Taste and flavour: mild salty taste when spices are not added. No off-flavour. Some rancid

flavour might occur.

Dried meat must be continuously examined for spoilage-related off-odour, which is the result of

incorrect preparation and/or drying of the meat. Meat with signs of deterioration must be rigorously

sorted out.

Packaging and Storage

This serves to protect against contamination. Paper, plastic foils, aluminium foils, cellophane and

textiles. Vacuum packaging gives longer shelf-life. Cardboard can be used. Prevention of wet

condition setting in order to prevent bacteria and mould under storage is important.

Meat drying in combination with additional treatment

i) Pre-salting ii) cured dried meat iii) smoked dried meat iv) dried meat with spices and additive e.g

Kilishi

Meat Preservation by Thermal Treatment

Characteristics of Heat-Treated Preserved Meat and Meat Products

The prolonged shelf-life of heat-treated meat and meat products is achieved through reducing

growth of, or inactivating, micro-organisms by a thermal process. The principal steps of the heat

preservation method are to:

place the product in a container (can, glass jar, pouches of synthetic material or laminate

with aluminium) which is hermetically sealed after filling and which is impermeable to any

external substances; and


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submit the hermetically sealed product to thermal treatment with a defined temperature

and time combination.

Equipment for Thermal Treatment

Thermal or heat treatment is done by submerging the products in cooking vats or pressure cookers

which contain hot water or steam or a mixture of both. It can be performed under pressure in

pressure cookers (retorts, autoclaves) in order to reach temperatures above 100°C (“sterilization”).

Sterilization is the most important and efficient type of heat treatment, since foods free from viable

micro-organisms can be obtained and most of these products can then be stored without

refrigeration. In contrast, temperatures up to 100°C can be achieved in simple cooking vats

(“pasteurization”). A certain amount of micro-organisms resist this moderate heat treatment and the

resulting pasteurized products must consequently be stored under controlled temperatures.

After thermal treatment the product must be chilled as quickly as possible, in order to avoid

overcooking. Hence, this operation is done within the cooker by introducing cold water. The contact

of cold water with steam causes the latter to condense with a rapid pressure drop in the retort. A

high pressure difference between the cooker and the internal pressure in the containers must be

avoided in order not to induce permanent deformation or damage of these containers.

Containers for Thermally Treated Preserves

Containers for heat-preserved food must be airtight in order to avoid recontamination by

environmental microflora. Moreover, no traces of undesirable substances which the packaging

material may contain, such as heavy metals (lead, tin), should be permitted to migrate into the

product. Currently, most of the thermally preserved products are:

i. Cans,

ii. Glass jars or plastic or

iii. Aluminium/plastic laminated pouches.

The advantages of aluminium cans are low weight, resistance to corrosion, good thermal

conductivity and recyclability, but these cans cannot be soldered or welded. They are less rigid and

more expensive than steel plate.

Meat Products Suitable for Canning

cooked ham

sausages with brine of the frankfurter type

sausage mix of the bologna or liver sausage type

meat preparations such as corned beef, chopped pork, etc.


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ready-to-eat dishes with meat ingredients such as beef in gravy, chicken with rice, etc.

soups with meat ingredients such as chicken soup, oxtail soup, etc.

Organoleptic, Physical and Microbiological Aspects of Thermal Treatment

The intensity of heat treatment has not only a decisive impact on the inactivation of micro-

organisms, but also on the organoleptic quality of the product. As a result:

1) There are products which undergo intensive temperature treatment without significant

losses in quality.

2) Some other products may deteriorate considerably in taste and consistency after

sterilization. In these cases less intensive thermal treatment is required but, at the same

time, other hurdles, such as low pH value and/or water activity or a lower storage

temperature, have to be built up in order to inhibit bacterial growth.

The intensity of thermal treatment can be defined in physical terms. The term widely used under

practical conditions is the F-value, with which the lethal effect of heat on micro-organisms can be

defined. The thermal death time for different micro-organisms calculated at 121°C and expressed in

minutes, is used as the reference value.

The thermal death time for spores of Clostridium botulinum at 121°C is 2.45 minutes or in other

words, an F-value of 2.45 is needed to inactivate all these spores in the product at 121°C. Spores of

other micro-organisms are more or less heat resistant. Vegetative cells of micro-organisms are

generally destroyed at temperatures of less than 100°C and therefore play no role in the F-value

calculations. The definition of the F-value at121°C is as follows:

F = 1: lethal effect at 121°C on micro-organisms after 1 minute

F = 2(3, 4, etc.): lethal effect at 121°C on micro-organisms after

2(3, 4, etc.) minutes.

The lethal effect can be shown in the reduction (in percentage) of the total number of micro-

organisms present in the product. The destruction of micro-organisms is at an exponential rate,

which means that the higher the initial bacterial load (using the same time-temperature

combination), the higher the number of surviving bacteria.


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Table 1. Decimal reduction rates during heat treatment

Remaining micro-organisms

Initial bacterial load (micro-organisms/g) 1St Treatment 2nd Treatment 3rd Treatment

10 million 1 million 100 000 10 000

1 million 100 000 10 000 1 000

100 000 10 000 1 000 100

10 000 1 000 100 10

1 000 100 10 1

The initial bacterial load and the destruction rate are shown in Table 1. The table demonstrates the

importance of proper meat hygiene. Highly contaminated raw material with bacterial loads of 10

million per g will, even after intensive heat treatment, still give final products with a rather limited

shelf-life because of the high remaining rate of contamination.

Since the heat treatments will in many cases not be intense enough to destroy all spores, it is

important that cans be chilled as rapidly as possible after retorting and that storage temperatures

generally not exceed 20 to 25°C.

The nature of the heat-preserved product, its pH, amount of salt and other curing agents, and the

number of spores present, together with retorting time and temperature, determine the degree of

commercial sterility and product safety. It has been shown that F-values of 4 in heat-preserved

products will guarantee commercial sterility. Products with F-values below this level need additional

measures such as lowering the pH or refrigerated storage for their microbiological safety.

Micro-organisms have two adverse effects in improperly treated heat-preserved products:

organoleptic deterioration through protein degradation;

food poisoning by bacteria and/or toxins.

Categories of Heat-Treated Preserves

Pasteurized products

This requires only slight thermal treatment. Temperatures reached in the product centre are in the

range of 82°C and below 100°C (“pasteurization”). The F-value cannot be determined, remaining

almost at zero.


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Inactivated: most vegetative micro-organisms

Not inactivated: spores of Bacillus and Clostridium

Storage required: uninterrupted cold chain (2–4°C), up to six months

Cooked preserves

This refers to thermal treatment only with boiling water (no pressure cooker).

Temperature reached in the product centre is up to 100°C. Low F-value.

Inactivated: all vegetative micro-organisms

Not inactivated: spores of Bacillus and Clostridium

Storage required: not higher than 10°C for one year. Spores will not grow under these conditions.

“Three-quarter” preserves

This refers to thermal treatment in pressure cooker. Temperatures reached in the product centre

are between 108 and 112°C. F-value 0.6 to 0.8.

Inactivated: all vegetative micro-organisms, spores of Bacillus

Not inactivated: spores of Clostridium

Storage required: not higher than 15°C for one year. Spores of Clostridium will not grow under

these conditions.

“Full” preserves stable under temperate conditions

This is Intensive thermal treatment in pressure cooker. Temperature reached in the product centre is

about 121°C. F-value 4 to 6 (“sterilized product”).

Inactivated: all micro-organisms except thermophilic spores

Storage required: ambient temperature (for one year), but not tropical conditions (40°C or

more).

“Full” preserves stable under tropical conditions

Very intensive thermal treatment, with a long period of 121°C or higher in the product centre. F-

value of 12 and more.

Inactivated: all micro-organisms including thermophilic spores

Storage required: ambient temperature even under tropical conditions (up to four years).

Shelf-stable preserves

This group of preserves is different from those mentioned previously, since preservation is achieved

not only by thermal treatment, but also by utilizing other means to prevent microbiological growth

such as nitrite, low water activity and/or low pH. This combined effect has the advantage of a fully

shelf-stable product under all ambient conditions without undergoing intensive thermal treatment

(less than 100°C) and without major losses in organoleptic quality.


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Factors Affecting the Shelf-Life of Meat and Meat Products

Though meat handling, storage and consumption may differ from one place to another, the factors

limiting the shelf-life of these products are the same.

There are endogenous factors, such as:

pH-value or the degree of acidity of the product;

aw value or the amount of moisture available in the product; and exogenous factors, such as:

oxygen (from the air);

micro-organisms;

temperature;

light; and

evaporation and desiccation.

Pre - Slaughter Handling of Different Farm Animals

What is pre-slaughtering handling?

It is the way in which an animal is treated before being killed and after and this affects the post-

mortem changes and the quality of meat.

N.B. in other words how the preparation made prior to few hours to slaughtering affects the farm

animals and quality of meat produced. We want to discuss what happens when an animal is being

moved farm to the slaughtering pen.

When animals are moved to unfamiliar surroundings, they may become excited, fatigue, overheated

or chilled. All these conditions result from response within the animal body caused by various factors

in the new environment. Hence referring to such reactions of animals under those conditions it is

often noted that such animals are expressing stress.

The term stress is an expression referring to the physiological adjustments, such as the changes in

heat rate, respiration rate, body temperature, and blood pressure that occur during the exposure of

the animal to adverse conditions. Such conditions called STRESSORS. occur when the environment

becomes uncomfortable or hazardous to the animal e.g Temperature, humidity, light, sound and

space.


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Physiological Responses during Stress

Naturally the animal body has a store of many natural defences against adverse conditions and

those defences attempt to maintain those internal conditions that enable the animal to continue its

life process (Homeostasis).

The adjustments in metabolism that occur during periods of stress are aided by the release

of certain hormones. Hormones of importance are EPINEPHRINE and NOREPINEPHRIN from the

adrenal medulla, ADRENAL STEROIDS from the adrenal cortex and THYROID HORMONES from

thyroid glands. The adrenal hormone provides stress resistance.

Epinephrine helps break down the glycogen that is stored in the liver and muscle as well as

the fat that is stored in several locations in the body in order to provide a ready sense of energy.

EPINEPHRINE and NOREPINEPHRINE helps to maintain proper blood circulation by their

influence on the heart and blood vessels hormones from the adrenal cortex are also effective in

reinforcing the ability of the tissues to respond during stress. Thyroid hormones increase metabolic

rate and thereby provide increased available energy to the animal.

Factor That Causes or Contribute to Stress

1. Environment Factors e.g. temperature, humidity, light, sand and space.

2. Transportation of the animals: it is during transit that most death losses and tissue bruising

occurs also muscle tissue shrinkage and reduction of weight of the dressed carcass can result

from severe live weight in the marketing process, due to loss of gastro-intestinal tract

contents.

3. Overcrowding

4. Poor ventilation

5. Mixing of unfamiliar animals

6. Physical discomfort

7. Excessive noise

8. Loading and Unloading animals by means of steep ramp or steps.

Remedy

1. Holding livestock in a stocky and prior to slaughter provides opportunity for resting and

feeding. In addition it helps to improve the ability of the animal to withstand later handling,

this in cow can influence the level of energy stored in the muscle.

2. Animals should not be manhandled. The use of sticks and whops should be discouraged.


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3. Different social group of animals should not be mixed together, overcrowding should be

avoided.

4. Animals should not be slaughtered immediately on arrival from long treks but should be

rested in Lairage for at least 24hours.

5. Diseased animals should not be slaughtered.

Pre Slaughtering Handling from the Lairage to the Stunning Pen

Animals should be pasted for 12 – 16 hrs before slaughter to reduce the amount of undigested food

and faeces in the intestine. Fasting also improves the quality of meat and reduces risks of

contamination of the carcass by practice during evisceration

Animals to be held for more than 24hrs should be provided for with light feeding. If pigs are deprived

of feed and water for more than 24hrs they may be unsuitable for the production of sausage or ham.

From the holding yard, the animal should move through a clinte narrow enough to prevent turning

and which should lead into a stunning pen.

Stunning is rendering an animal unconscious before being bled.

Requisites for Satisfactory Stunning Are

1. Quick rendering of unconsciousness without abuse or mutilation and

2. The prolongation of unconsciousness until the animal has bled out. Death should come

instantaneously and without visible preparation to the animal.

For species like poultry:- they need to be rested in a good place and have access to water with no

food for about 12 hours. Late feeding prevents good bleeding and makes the intestine tear easily

during evisceration

Slaughtering Methods/ Techniques

There are two common method of slaughtering

i) Muhammedan method: is a common method in Nigeria. About 99% of abattoirs use the

above method and in some countries the method is used on emergency cases. The 4 – legs are tied

with rope. The animal is placed facing the eastern part as the butcher says some prayers before

cutting the carotid artery and jugular vein. The positioning of the animal is called prone carcass.

Disadvantages

1. There can cause injury to the handler

2. Damage of hides and skin

3. It can serve as a source of entry to microbes which can cause PUTRIFACTION .

4. There is possibility of incomplete bleeding


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ii.) Humane Method: quality of kindness

A stunning pen may be about 2.25m in length and 1m wide. If a stunning pen is not possible, a ring

emplaced in the floor of the slaughtering house may be used to secure the animals head and this is

in sure accuracy of the blow for stunning. The ring should be located where the animal does not see

carcasses and where the floor is not slippery.

Stunning Methods

1. Use of Gas: Here the gas used is CO2 the animal is lead into the air tight chamber and the

within seconds it becomes unconscious.

2. Electric Appliance: The use of electricity for stunning has become the recommended

practice. Electricity is applied with a prior of tons. For pigs the tongs are applied immediately

below the ears for 6-10 secs. With a current of 60-70 volts the time and voltage is similar for

calves and sheep but the tongs are applied between the eye and the ear.

3. Captive Bolts Pistol: it protects on cartridges. It is directed to the frontal lobe. It is often

used for the big animals like bulls.

4. Hammer: it also directed on the frontal lobe of the animals. It is also used for big animals.

Slaughtering Stages or Abattoir Operations

Pre inspection stunning bleeding (hoisting)

Bleeding:- cattle throat is slashed where the vena cava, jugular veins and carotid arteries are

situated.

Sheep and Goat:- a stuck behind the jaw below the ear

Pigs:- incision are made approximately 5cm above the breast bode on the front of the neck and the

knife thus towards the entrance to the chest, cutting the carotid arteries and jugular veins.

scalding or skinning evisceration splitting of carcass into 2 equal halves

Post-inspection washing with warm water wipe dry chill

Post Mortem Changes in Meat/Conversion of Muscle to Meat

The conversion of muscle to meat involves a number of physical and chemical changes which take

place over a period of several hours or even days. The maintenance of a physiologically balanced

environment is termed HOMEOSTASIS. This could be regarded as a system that ensures uniformity

and stability of the internal environment thereby providing the body with a means of coping with

abnormal (stressful) conditions.


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1.) Exsanguinations: Is the act of removing as much blood as possible from the animal. The loss

of blood and resultant loss in blood pressure sends signals to the circulatory system via the brain and

it adjusts its function in an attempt to maintain a blood supply to the organs. Exsanguinations marks

the beginning of a series of post mortem changes in the muscle only about 50% of the total blood

volume can be removed from the body, the remainder is held mainly in vital organs.

2.) Circulatory Failure to the Muscles

The function of the circulatory system is to transport essential nutrients to the muscle and carry

waste products away from the muscle, but exsanguinations eliminates this line of communication

between the muscle and its external environment.

In the living cell of a living animal, O2 is picked up in the lungs and carried to the cells of the body by

the haemoglobin pigment of the blood. The myoglobin of the muscle cells has a greater attraction

for O2 than does haemoglobin, a characteristic that helps transfer O2 from the blood of the muscle

cells. The myoglobin provides a place for storing the O2 until it is used by the cells for metabolism. As

the stored O2 supply becomes depleted after exsanguinations the aerobic pathway through the

citrate cycle and the cytochrome system must stop functioning. Energy metabolism is then shifted to

the anaerobic pathway considerably less energy that will maintain the structural integrity and

temperature of the cells for some time.

3.) pH Decline:- Since the circulatory system is no longer functioning lactic acid produced by

anaerobic metabolism, instead of being transported to the liver for the synthesis of glucose and

glycogen remains in the muscle and increases in concentration as metabolism proceeds. The lactic

acid produced causes the lowering of the pH in meat, making the meat acidic. Thereby cause the

denaturing of muscle proteins leading to loss of water holding capacity and the result is a muscle

with pale colour. The pH of a living muscle from pork decrease from pH 7 to about 5.6 -5.7 within 6 -

8 hours post-mortem and then to an ultimate pH (reached after 24hours post-mortem) of about 5.3

-5.7. Muscle which have a very rapid and extensive pH decline will be pale in colour, will have very

low WHC on the other hand, muscle to meat will be very dark coloured and very dry on the exposed

cut surface because the naturally occurring water is tightly bound to the proteins.

4.) Post-Mortem Heat Production and Dissipation

As a result of exsanguinations and circulatory failure heat can no longer be carried to the lungs and

other surface areas for dissipation, therefore causing a rise in muscle temperature. External factors

associated with the slaughter process will also influence heat dissipation such as ambient

temperature in the slaughter room, the length of the slaughter and dressing operation and the


21

temperature of the initial chill cooler will all have a considerable influence on the rate of carcass

temperature decline.

5.) Rigor Mortis (Latin: “Stiffness of Death”)

This is the stiffening of the muscle after death and is due to the formation of permanent cross-

bridges in the muscle between the actin and myosin filaments. During the period immediately

following exsanguinations muscle is quite extensible, if a force is applied to it the muscle will

passively stretch and when the force is removed, then natural electricity of the muscle will return to

its original length. At that time only few actomyosin is present to prevent extension by a force. The

period of time during which the muscle is relatively extensible and elastic is called DELAY PHASE OF

RIGOR MORTIS

The Onset Phase of rigor mortis begins when the muscle begins to lose extensively only in ensuring

relaxation which the actomyosin bond. Rigor mortis therefore is an irreversible muscle contraction

ADP -------- ATP + Energy.

When muscle glycogen stores is depleted, ATP produced becomes insufficient to maintain the

muscle in a relaxed state.

6.) Loss of Protection from Bacteria Invasion

During the conversion of muscle to meat, following exsanguinations, the antimicrobial defence

system ceases to function, membrane properties are altered and the muscle becomes susceptible to

bacterial invasion unchecked.

7.) Enzymatic Degradation

In the muscle cells, proteolytic enzymes called cathepsins are held in an inactive state in organelles

called lysosomes. The drop in pH at the death of the animal activities these enzymes and they begin

to degrade the protein structure of the muscles. In addition the muscle proteins may be subjected to

denaturation due to pH drop.

Relation between Ph Decline and the Development of Rigor Mortis

Muscle with a normal pH decline curve will have on poultry meat has been shown to be due to

induction of rapid outset of rigor mortis and most directly related to the rapid pH decline of the

meat while carcass is still warm. Beginning immediately after death, CP falls rapidly with pH

following the same pattern as ATP levels. ATP breakdown now commences and proceeds rapidly

until the level becomes low. As ATP levels declines, there is rapid decrease in muscle extensibility.

Stress affected meat becomes dark, blue –red in colour.


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8.) Changes in the Physical Appearance of the Muscle

In living animals muscle with sufficient oxygen supply has a bright red appearance. In post mortem

muscle, as the O2 is used, the muscle becomes dark purplish red in colour. The lower the pH the

lower the water binding properties of meat.

Cold Shortening

Muscles shorten as permanent bonds form during the development of rigor mortis. Minimum

shortening occurs at 14o c to 19 o C. If the temperature of the muscles is reduced to below 10 -16 o C

while they were still in the early pre-rigor condition (pH 6.0 – 6.4), there is a tendency for shortening

and thereby toughness in cooking. This phenomenon is referred to as Cold Slaughtering.

Thaw Rigor

This is the shortening that occurs upon thawing meat that was frozen in the pre –rigor state. The

onset of thaw rigor occurs while the amount of ATP is relatively high (40 o c); meat becomes less

tender. In case meet is not allowed to complete its rigor months before freezing, the meat should be

rapidly thawed before using, since slow thawing with accumulation of a high concentration of salts

in the thawed fluid appears to accelerate thaw rigor.

Ageing Meat

in the absence of microbial spoilage the holding of unprocessed meat above freezing point ( usually

2-5 o c) for about 2- 4 weeks is known as CONDITIONING OR AGEING OR RIPENNING, this practice

helps to increase tenderness and flavour.

Meat Quality

Meat quality refers to the condition of meat. Meat quality refers to a combination of traits that

provide for an edible product that is attractive in appearance, appetizing, nutritive and palatable

after cooking. The ideal level of meat quality combines the capacity to retain a high nutritive value in

the cooked form with that to excel in satisfying numerous functional roles in the fabrication and

processing of acceptable products. In determining the quality of meat parameters to look out for

are:-

a) Colour (Appearance)

Appearance is a very vital component that strongly affects the consumer acceptability of fresh meat.

The colour of fresh meat is determined by myoglobin and haemoglobin.


23

Dark Firm and Dry (DFD) and Pale Soft Exudative (PSE) are meat with pale colour as well as soft

watery texture. DFD meat has a high pH which is above iso-electric point of actomyosin. It has an

unpleased purplish-red colour of myoglobin and thus the meat appears dark. PSE pork comes from a

rapid and severe post-mortem drop in pH resulting in denaturing of sarcoplasmic and myofibrillar

proteins in the muscle. Factors that affect colour are:

a) Age of the animal

b) The type of muscle involved

c) Degree of surface desiccation

d) Temperature

e) Bacterial growth

b) Texture: Meat that contains a high degree of marbling will be firmer than meat with little

marbling muscles that are rough and coarse are of pork textural quality.

c) Tenderness: It is a sensation created. It is a complicated physical process, since chewing involves

cutting, grinding, squeezing, shearing and tearing. Tenderness is measured by means of

a) Shear press

b) Instron which is used in measuring textural properties of frozen and freeze – dried broiled

meat.

c) A sensory test which requires taste panel.

Factors affecting tenderness include;

1. Age and maturity

2. Activity: strengthen and toughen muscle – tissue

3. Nutrition:- degree of fatness, processing, pre slaughter husbandry, chilling, scalding, ageing

and freezing, sex of animal

d) Flavour: This is the combined effect of food on the sense of taste, odour and mouth-feel. Hence

the evaluation of flavour is subjective. Flavour is the mixed sensation of aroma and taste by

which individual foods are identified.

Methods of Meat Preservation

Preservation is defined as any method of treating food to prolong the length of time in which it

retains its quality and appeal. Methods of preserving meat include refrigeration, freezing, thermal

processing and dehydration. Following exsanguinations the process of converting muscle to meat. It

begins by subjecting the meet to degradation by chemical, physical, enzymatic and microbiological

reactions. Preservation is to prevent degradation from taking effect.


24

1) Cold Storage

I. Chilling Storage:- is generally regarded to be storage at temperature not far above freezing

(0 o c)s e.g. temperature ranging from 0 O C to 1.1 o C can chill the thickest part of carcass between 12

-21 hours which can be stored for 8 days for beef, 6 days for lamb. Temperature between 5 o c – 10 o

c is limited to short period of storage.

II. Freezing:-

a) Slow freezing:- Involves freezing with only natural air circulation or at best with electric fans.

Temperature is usually -23.3 o c or lower and freezing may take from 3 to 72 hours.

Large ice crystals are usually formed within the muscle fibre. Ice crystals are usually needle

like which are capable of destroying muscle fibre. There is much fluid loss

b) Quick /fast freezing: is accomplished either by

i) Direct immersion of food in a refrigerant e.g. freezing of fish in brine.

ii) In direct contact with the refrigerant where the food or package is in contact with the

passage through which the refrigerant at -17.8 - -45.6c flows or

iii) By air-blast freezing, where frigid air at -17.8 - 34.4c is blown across the materials being

frozen

2. Dehydration Method:- Removal of water by

i. Sun Drying:- weather must be warm and dry. The demerit of this method is that it is subject

to weather condition and is contamination from dust and sand.

ii) Hot air drying:- only applicable to cooked meat.

iv. Salting: its diffusion in meat is by the process of osmosis. It improves the texture of meat

and contribute to the pleasant flavour and aroma of the product. It inhibits the growth of

bacteria although there are some salt tolerant bacteria.

iv) Smoking:- It decrease the more - soluble protein (myofibrillar and sarcoplasmic) content

while increasing the amount of the more - insoluble (stomach) proteins.

v) Meat curing: - is an aspect of meat preservation in which salts, sugars nitrite/ nitrate,

phosphate and other curing agents are used to improve meat colour and its acceptability

after slaughter

Curing Ingredient

1. Salt (NaCl)

2. Sugar and corn syrup solids:- sugar is added to curves for its moderating action on flavour

and to soften the products by counteracting the harsh hardening effects of salt by

preventing some of the moisture removal. Corn syrup, corn syrup solids (corn syrup from


25

which most of the water has been removed) molasses and other natural sugar substitutes

are sometimes used in place of sugar. Corn syrup consists of sugars formed by the

breakdown of starch and contains dextrose maltose, higher sugars, dextrin, and

polysaccharides CS is not so sweet and is less soluble than sugar.

3. Nitrate

- To stabilize the pink colour of the lean tissue

- To contribute to the characteristics flavour of cared meat

- To retard the development of rancidity

- To inhibit the growth of a number of a number of food poisoning and food and food

spoilage organism e.g Clostridia botulinum

4. Phosphate

o To increase the water binding capacity

o Improve retention of brine.

o Improve colour and flavor retention

o Act as buffers

5. Ascorbates

- Salt of ascorbate acid are commonly used to hasten the development and stabilize the colour of

cured meat by

a) Taking part in the reduction of metmyoglobin to myoglobin

Monosodium Glutamate (MSG)

- To enhance flavor not widely used in the industry

6. Canning: can either be sterile or pasteurized

i.) Sterile Product: are shelf- stable and need no refrigeration e.g Luncheon meats, corned

beef and sandwiched spread are example of sterile products

ii.) Pasteurized Product:- Cooked ham.

Bulging cans could result to food poisoning e.g Clostridia botulinum. A disease condition as

BOTULISM

Symptoms

1. Dizziness

2. General weakness

3. Severe headache

4. Loss of vision

5. Paralysis of throat muscle


26

This is because the toxins are very lethal which can kill almost immediately. In respiratory center

leading to death, speech becomes impaired.

MEAT PROCESSING

Processed meat products are defined as those in which the properties of the fresh meat have been

modified by the use of one or more procedures such as grinding or chopping, addition of seasonings,

alteration of colour, heat treatment, drying and other processing /conservation processes.

Recipe

Meat 55 -65%

Seasoning 1-2 %

Additives 1-2 %

Fat 1-15%

Fillers/binders 20-25%

Water 13-15%

Seasoning - Coriander 70g, Nutmeg 40g, Mace 40g, pepper 115g, salt 200g,Monosodium

glutamate 5g

It adds to flavour to whatsoever is been prepared. Seasoning are added to sausage to perform

function like

i. Influence the flavour of the product

ii. Serves as preservatives

iii. Stimulate the production of digestive juices which aid digestion and absorption

iv. Influence colour and overall acceptability of the product

Additives

i. Chemical additives

ii. Natural additives

i. Chemical Additives

a) Polyphosphate

i) Increase water binding capacity

ii) Improve retention of brine

iii) Improves colour retention

v) They act as buffers


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b) Ascorbic acid

i) Use to hasten development and stabilize the colour of cured meat by –

a) Taking part in the reduction of metmyoglobin to myoglobin, thereby accelerating rate of

curring

b) React with nitrite to increase the yield of nitric oxide to for nitrous acid

c) Excess ascorbate acting as anti-oxidants, thereby stabilizing both colour and flavor

c) Monosodium glutamate:- they are needed to enhance flavour, but are not widely used in the

meat industry

ii. Natural Additives:- This could be of protein source e.g. egg powder

Fat:- Back fat, they play major role in texture juiciness and flavour of comminuted meat producs

Fillers and Binders:- they are basically carbohydrates and are starchy in nature e.g. wheat flour,

cassava flour etc.

a) To improve emulsion stability

b) To improve water binding capacity

c) To enhance flavor

d) To improve slicing characteristics

e) To reduce formulation cost i.e. it helps to add to the bulkiness of sausage

Water:-

a) Increases juiciness and palatability

b) Lowers the temperature of the product

c) Aids thorough chopping and mixing

d) Aids in dissolving salt

e) Influence the texture of sausage mix.

Sausage Casing

These are container use in packaging the comminuted meat and hold it together until its get to the

consumer. They determine the size and shape of the sausage. There are two types of casing, the

natural and the artificial casing

i.) Natural Casings:- From intestine and bladders of cattle, dogs, sheep, pigs etc.

a) This containers protect the meat from sudden loss of moisture

b) The container is digestible and shrinks with meat as its water content reduces

Because of rise in demand for sausage meat natural casing could no longer meat the

demand


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ii.) Artificial Casing:- They are either cellulose from cotton inters(cotton by-products) or

collagen (from the corium layer of beef hides). These casings can be made more uniform in

size and performance characteristics than animal casing

a) Cellulose:- it gives sausage and smoked meat the desired uniformity in diameter and

length and the stability to withstand modern high temperature and rapid processing

conditions . The advantages of cellulose casing are:

- Easy to handle and stuff

- Posses a high degree of resistance to breakage

- And permeable to smoke when moist

- Requires careful storage

- Humility is very critical since cellulose becomes quite brittle when very dry.

b) Collagen Casing

It was developed as edible casing similar to animal casing but possessing the uniformly

of a manufactured product. its best kept at a RH of about 40 -45%

EGG AS AN ANIMAL PRODUCT

FORMATION OF EGG

Figure 6: Reproductive tract of hen

The avian egg, in all its complexity, is still a mystery. A highly complex reproductive cell, it is

essentially a tiny centre of life. Initial development of the embryo takes place in the blastoderm. The

albumen surrounds the yolk and protects this potential life. It is an elastic, shock-absorbing semi-


29

solid with high water content. Together, the yolk and albumen are prepared to sustain life - the life

of a growing embryo - for three weeks, in the case of the chicken. This entire mass is surrounded by

two membranes and an external covering called the shell. The shell provides for an exchange of

gases and a mechanical means of conserving the food and water supply within

The egg is formed in the mature hen by a reproductive system composed of an ovary and oviduct.

Most females have two functional ovaries, but chickens and most other birds have only one ovary

and one oviduct. In this oviduct, all parts of the egg, except the yolk, are formed. It is divided into

five distinct regions: (1) infundibulum or funnel, (2) magnum, (3) isthmus, (4) uterus or shell gland,

and (5) vagina.

The yolk is formed in the follicular sac by the deposition of continuous layers of yolk material.

Ninety-nine percent of the yolk material is formed within the 7-9 days before the laying of the egg.

When the yolk matures, the follicular sac ruptures or splits along a line with few blood vessels. If any

blood vessels cross the stigma, a small drop of blood may be deposited on the yolk as it is released

from the follicle. This causes most blood spots in eggs. After the yolk is released from the follicle, it is

kept intact by the vitelline membrane surrounding it. The release of the yolk from the ovary is called

"ovulation." There is a small white spot about 2 mm in diameter on the surface of the yolk. This is

the germinal disk and it is present even if the egg is infertile. If the egg is infertile, the germinal disk

contains the genetic material from the hen only. If the egg is fertile, it contains genetic material from

both parents and is where embryonic development begins. The yolk material serves as a food source

for embryonic development.

After its release from the follicle, the yolk falls into the hen's abdominal cavity. The infundibulum of

the oviduct quickly engulfs the yolk with its thin, funnel-like lips. The yolk quickly enters the magnum

section of the oviduct where the dense portion of the albumen is added. The shape of the egg is

largely determined in this section.

The magnum of the oviduct is divided from the isthmus by a narrow, translucent ring without glands.

The isthmus is smaller in diameter than the magnum. It is here the two shell membranes form. The

shell membranes loosely contain the yolk and dense white until the rest of the albumen is added in

the uterus.

The egg white (albumen) is produced by the oviduct. There are four types of egg white. The outer

thin white is a narrow fluid layer next to the shell membrane. The outer thick white is a gel that

forms the centre of the albumen. The inner thin white is a fluid layer located next to the yolk. The

inner thick white (chalaziferous layer) is a dense, matted, fibrous capsule of albumen around the

vitelline membrane of the yolk. The matted fibrous capsule terminates on each end in the chalazae,


30

which are twisted in opposite directions and serve to keep the yolk centred. The chalazae are

twisted so that the germinal disk always orients itself upwards. During storage, however, the thick

albumen becomes thinner allowing greater movement of the yolk.

The shell is added in the uterus or shell gland portion of the oviduct. The shell is composed mainly of

calcium carbonate. It takes about 20 hours for the egg shell to form. If the hen lays brown eggs, the

brown pigments are added to the shell in the last hours of shell formation.

The chalazae, two cord-like structures which keep the yolk centred in the egg, first appear in the

uterus. The chalazae also function as an axis around which the yolk can rotate and keep the germinal

disc in hatching eggs uppermost at all times.

In the last portion of the oviduct, the vagina, a thin, protein coating called "bloom" is applied to the

shell. The cuticle somewhat seals the pores and is useful in reducing moisture losses and in

preventing bacterial penetration of the egg shell. Much of the cuticle is removed from table eggs

when they are mechanically washed. To replace the cuticle, table eggs are often sprayed with a light

mineral oil mist. The egg passes through the oviduct small end first, but is laid large end first. In the

vagina, the egg is turned horizontally just before laying. If the hen is disturbed on the nest, the egg

may be prematurely laid with small end first. "Oviposition" is the act of pushing the egg from the

oviduct.

When the egg is laid it is at the same temperature as the hen's body (about 105°F). As the egg cools

to ambient temperature, the egg contents contract and the two shell membranes separate,

generally at the large end of the egg, forming the air cell. The outer membrane sticks to the shell

while the inner membrane sticks to the albumen. During storage, the egg loses water by

evaporation, causing the air cell to enlarge.

Egg Formation Timeline

The average time an ovum spends in each structure as it passes down the oviduct

Infundibulum: about 15 minutes

Magnum: 2-3 hours

Isthmus: 1½ hour

Uterus: about 20 hours

Vagina: just a few minutes


31

Figure 2: diagram of an egg

Egg sizes

Eggs are sorted into five different sizes according to weight: Jumbo, Extra Large, Large, Medium,

Small, and Pee Wee. The following are the weight standards and approximate nutritional values

associated with each of these sizes:

UK egg sizes US egg sizes

New Size Weight Egg sizes Average weight

Very Large > 73g Jumbo 71g

Large 63 - 73g Extra-large 64g

Medium 53 - 63g Large 57g

Small


32

The nutritive content of an average large egg (containing 50 g of edible egg) includes:

6.3 g protein

0.6 g carbohydrates

5.0 g fat (this includes 0.21 g cholesterol).

Egg protein is of high quality and is easily digestible. Almost all of the fat in the egg is found in the

yolk and is easily digested.

Vitamins

Eggs contain every vitamin except vitamin C. They are particularly high in vitamins A, D, and B12, and

also contain B1 and riboflavin. Provided that laying hens are supplemented according to the

Optimum Vitamin Nutrition concept. Eggs are an important vehicle to complement the essential

vitamin supply to the human population.

Minerals

Eggs are a good source of iron and phosphorus and also supply calcium, copper, iodine, magnesium,

manganese, potassium, sodium, zinc, chloride and sulphur. All these minerals are present as organic

chelates, highly bio-available, in the edible part of the egg.

Egg Grades

Grading is a form of quality control used to divide a variable commodity or product into a number of

classes. The United States Department of Agriculture (USDA) standards for quality of individual shell

eggs were developed on the basis of both interior and exterior quality factors. Commercially, eggs

are graded simultaneously for exterior and interior quality. When determining the grade of an egg,

the factor with the lowest grade will determine the overall grade of the egg. In the United States,

egg grades include AA quality, A quality, B quality, and dirty. Only AA and A quality eggs are sold for

supermarkets.

Egg Quality

Egg quality is a general term which refers to several standards which define both internal and

external quality. External quality is focused on shell cleanliness, texture and shape, whereas internal

quality refers to egg white (albumen) cleanliness and viscosity, size of the air cell, yolk shape and

yolk strength.


33

Egg Size

The size of an egg is controlled by many factors. Among these factors including individual genetic

markers, stage of sexual maturity, age, drugs and some dietary nutrients available to the bird. The

most important nutritional factors known to affect egg size are protein and amino acid adequacy of

a diet and linoleic acid.

Egg Shell Quality

Shell colour comes from pigments in the outer layer of the shell. Shell colour is primarily a breed

characteristic, although there is often variation among individual hens in a particular flock even

when all are of the same breed and variety. Egg shells of commercial breeds of chickens are white or

brown. Breeds with white earlobe ordinarily lay white eggs while breeds with red earlobes ordinarily

lay brown eggs. White eggs are most in demand among American buyers. In some parts of the

country, however, particularly in New England, brown shells are preferred. The Rhode Island Red,

New Hampshire and Plymouth Rock are breeds that lay brown eggs. Since brown-egg layers are

slightly larger birds and require more food, brown eggs are usually more expensive than white.

While darker coloured brown eggs tend to have thicker shells, shell colour has nothing to do with

egg quality, flavour, nutritive value, or cooking characteristics.

The appearance of the egg, as influenced by severity of defects, is important for consumer appeal.

Egg shells are evaluated on the basis of cleanliness, shape, texture, and soundness.

Cleanliness

Most eggs are clean when they are laid, but they can become contaminated with manure or other

foreign material. In the United States, an egg with manure or adhering material on the shell cannot

be marketed. It is classified as dirty and cannot be used for human consumption. Eggs with stained

shells are unattractive in appearance and cause eggs to be downgraded to B quality or dirty

depending on the severity of the stain.

Shape

The "normal" chicken egg is elliptical in shape. Eggs that are unusual in shape, such as those that are

long and narrow, round, or flat-sided cannot be placed in Grades AA or A. Round eggs and unusually

long eggs have poor appearance and do not fit well in cartons so are much more likely to be broken

during shipment than are eggs of normal shape.

Texture

An egg shell that is smooth is preferred since rough-shelled eggs fracture more easily and have poor

appearance. Eggs with extremely rough or uneven shells are downgraded to B quality. Some eggs


34

have a rough pimply appearance. The pimples (calcium deposits) are distortions to the shell.

Infection is not responsible because pimpling also occurs in disease-free flocks. The defect may be

partly hereditary.

Mottled shells have pale translucent spots (sometimes called "windows") of various sizes. Such eggs

appear normal when laid. The mottling develops later and may be noticeable half an hour after

laying, although it is more easily detected a day later. This abnormality is inherited, although a

similar effect can be induced artificially, such as when a wet, newly laid egg slides across the wire

cage floor instead of rolling, or when a hen's toenail scratches the surface of a recently laid egg.

Soundness

"Body checks" are eggs with shells that have been cracked during shell calcification in the hen and

have had a layer of calcium deposited over the crack(s) before the egg is laid. Some body checks are

covered by a relatively thick layer of calcium before being laid so are not easily detected unless eggs

are candled. Other body checks are only covered by a thin calcium layer before being laid so they are

easily detected.

The incidence of body checks will increase if hens are excited in the afternoon or early evening just

as the egg shell begins to form in the oviduct. It is important, therefore, to keep hens as calm as

possible, especially during the late afternoon and at night.

Body checks sometimes appear as ridges or bulges on the shell. Depending upon the extent and

severity of the ridge or bulge, or the ease of detecting the checked area, body checks may be

classified as B quality. These shells are usually weaker than normal shells, are more likely to break in

shipment, and they lack consumer appeal.

Sometimes eggs have thin spots in the shell. The thin spots may appear gray and the shell is more

likely to break in these areas.

Factors Affecting Shell Quality

Poor shell quality can result in downgrading. Producers should be aware of these factors so they can

take preventive actions to minimize the occurrence of costly downgrades. Management plays an

important role in controlling all of these factors to produce eggs of high quality. To assure the

production of high quality eggs, one should select a strain of birds known to produce eggs of good

quality because egg quality is a heritable characteristic. Avoid prolonged periods of temperature

above 86°F in the laying house, if possible. Use high quality feeds and adjust feed formulations

according to feed intake and the age of the hens. Practice the necessary steps to prevent disease

and other physiological disturbances in the flock. The time pullets start to lay can be regulated by


35

controlling feed and light in a planned program. Because egg quality decreases with the age of the

hen, the number of years to keep a hen should be considered in relationship to all aspects of the

production plan.

If one disease had to be singled out as being responsible for the majority of the economically

significant production losses in egg layers, it would be infectious bronchitis. Not only is egg shell

quality affected, but internal egg quality also declines. Watery whites are very common and can

persist for long periods after egg production returns. Also, an infectious bronchitis outbreak can

result in a pale-coloured shell in brown eggs. However, other factors, such as stress, are also

responsible for causing a pale-coloured shell.

Another disease which may affect shell quality is Egg Drop Syndrome 76 (EDS 76). EDS 76 was first

identified in Britain in 1976. A vaccine was quickly developed and the disease seemed to disappear.

However, it has recently reappeared in the Netherlands. The disease is mainly characterized by a

drop in egg production early in lay, or by a sudden fall in production at a later stage in the laying

period. In the beginning the symptoms include shell-less eggs and thin-shelled eggs, deformed eggs,

and, in the case of brown eggs, a loss of shell colour. In addition, the whites of these eggs are very

watery, and there is considerable variation in egg weight.

Internal Egg Quality

Interior egg quality is based on air cell size, albumen quality, yolk quality, and the presence of blood

or meat spots.

Albumen Quality

The albumen has a major influence on overall interior egg quality. Thinning of the albumen is a sign

of quality loss. When a fresh egg is carefully broken out onto a smooth flat surface, the round yolk is

in a central position surrounded by thick albumen. When a stale egg is broken out, the yolk is

flattened and often displaced to one side and the surrounding thick albumen has become thinner,

resulting in a large area of albumen collapsed and flattened to produce a wide arc of liquid.

Properly refrigerated eggs stored in their carton in a home refrigerator will change from AA-grade to

A-grade in about 1 week and from A-grade to B-grade in about 5 weeks. However, a properly

handled and refrigerated intact egg will retain its nutritional value and wholesomeness for a

considerably longer time.

Egg yolk from a newly laid egg is round and firm. As the egg gets older, the yolk absorbs water from

the egg white, increasing its size. This produces an enlargement and weakness of the vitelline

membrane; the yolk looks fl at and shows spots. As soon as the egg is laid, its internal quality starts


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to decrease: the longer the storage time, the more the internal quality deteriorates. However, the

chemical composition of the egg (yolk and white) does not change much. Increases in albumen pH

are due to CO2 loss through the shell pores, and depend on dissolved CO2, bicarbonate ions,

carbonate ions and protein equilibrium. Bicarbonate and carbonate ion concentration is affected by

the partial CO2 pressure in the external environment.

In newly laid eggs, the yolk pH is in general close to 6.0; however, during storage it gradually

increases to reach 6.4 to 6.9. Egg quality preservation through handling and distribution is

dependent on constant care from all personnel involved in these activities. The quality of the egg

once it is laid cannot be improved, so efforts to maintain its quality must start right at this moment.

The decrease in internal egg quality once the egg is laid is due to the loss of water and CO2. In

consequence, the egg pH is altered, resulting in watery albumen due to the loss of the thick albumen

protein structure. The cloudy appearance of the albumen is also due to the CO2; when the egg ages,

the CO2 loss causes the albumen to become transparent, compared with fresh eggs.

To minimize egg quality problems two things are important: frequent egg collection, mainly in the

hot months, and rapid storage in the cool room. The best results are obtained at a temperature of

10 °C. There are six main factors affecting internal egg quality: disease, egg age, temperature,

humidity, handling, and storage.

Disease: Newcastle disease and infectious bronchitis produce watery albumen, and this condition

may persist for long periods after the disease outbreak has been controlled.

Egg age: Eggs of several days’ old show weak and watery albumen and the CO2 loss makes the

content alkaline, affecting the egg flavour.

Temperature: high temperatures cause a rapid decrease in internal quality. Storage above 15.5 °C

increases humidity losses.

Humidity: high relative humidity (RH) helps to decrease egg water losses. Storage at an RH above

70% helps to reduce egg weight losses and keeps the albumen fresh for longer periods of time.

Egg handling: rough handling of the eggs not only increases the risk of breaking the eggs, but also

may cause internal egg quality problems.


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Storage: eggs are very prone to take on the odours of other products stored with them; separate

storage is therefore advised.

The variables mentioned above are particularly important to ensure that a 1-week-old egg, properly

handled, can be as fresh as a day-old egg kept at room temperature. If the egg is properly handled

during shipment and distribution, it will reach the consumer’s table with adequate freshness.

Storage of Eggs

1. Store eggs small end down in an egg carton to keep the air cell stable.

2. Date carton so you can use or sell the oldest eggs first and rotate your extra eggs. Try to use

or sell all eggs before they are three weeks old.

3. Store eggs at 50-55oF and 70-75% relative humidity.

4. Never store eggs with materials that have an odour. Eggs will pick up the odours of apples,

fish, onions, potatoes and other food or chemicals with distinct odours.

5. Never hold eggs at or above room temperature or at low humidity more than necessary.

Leaving eggs in a warm, dry environment will cause interior quality to drop quickly.

How to Tell if Eggs are Still Good

Have a carton of eggs that have passed their use-by date? Here's how to test to see if they are still

good. *Fill a bowl with cold water and place your first egg inside. If the egg sinks to the bottom, it's

fresh. If the egg sinks to the bottom, but stands on its point, it's still good but needs to be used soon.

If the egg floats to the top, it needs to be discarded.

Uses of Egg

Binder: One of the uses of eggs is as a binder. A binder helps other ingredients bind together (eggs

are used to help bind together meatballs, meatloaf and flour mixtures). When eggs are heated

they coagulate, this helps stick together the ingredients they are mixed with.

Coating: Another use of eggs is as a coating agent. The breading on fried chicken sticks because

the chicken is dipped into an egg then a flour or crumb mixture. The eggs help hold the crumb

mixture to the food when heated during the cooking process.

Thickening: Eggs have thickening properties. The protein in eggs will thicken when heated and

become firm. If an egg is overheated or cooked for too long of a time it will become rubbery and


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tough in texture. Eggs are often used in custards and sauces to thicken the finished product.

Emulsifier: Eggs are an emulsifier. An emulsifier permits small globules of one liquid to be inter-

dispersed in another liquid. For example in mayonnaise the egg acts as an emulsifying agent in

keeping the oil and vinegar mixed as one product and not separating out. Eggs also are emulsifiers

in cakes.

Crystallization: When a liquid freezes, ice crystals form. When eggs are added to a mixture, it

helps prevent these crystals from forming. That is why another use of eggs is the prevention of

crystallization.

Clarifier: The one use of the egg you probably are not very familiar with is using eggs as a clarifier.

The egg is used to make a broth clear. Any unwanted particles in the broth will stick to the egg as

it coagulates in the broth. The cooked egg is then removed.

Leavening: One of the most common uses of eggs is as a leavening agent. A leavening agent

helps to make a cooked product rise. When eggs are beaten they hold air. When heat is added

the structure will coagulate and traps the air. This is what gives angel food cakes, meringues and

soufflés their light and fluffy texture.


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EGG POWDER PRODUCTION • Egg Products Processing and distribution Module

Eggs from Production Farm

Saline test

Breaking

Homogenization Pasteurization(liquid eggs only)

Spray Drying

Cooling

Milling

Packaging


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Summary tableProcessed Egg Products

Product Use Properties

Liquid Whole Egg Bakery products, Omelette mix, Pie Filling

Liquid Egg White (Albumen) Bakery products, high protein foods, sausages etc

Binding, whipping

Liquid Egg Yolk (Yellow) Salad Dressings, Sauces, Mayonnaise Emulsifying

Frozen Salted Yolk Salad Dressings, Sauces, Mayonnaise Emulsifying

Frozen Salted Whole Salad Dressings, Sauces, Mayonnaise Emulsifying

Frozen Sugared Yolk Bakery Items Emulsifying

Frozen Whole Egg Replacement for Shell or Liquid Egg

Dried Egg Whites Replacement for Fresh Egg White in bakery products, high protein foods, sausages etc

Binding, whipping

Dried Egg Yolks Replacement for liquid or frozen yolks Emulsifying


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MILK

• Definition.: It is a white liquid produced by mammals and it is drunk by people

• Facts about Milk

• It is the source of nutrients and immunological protection for the young animals such as calf

and kid.

• Shortly before parturition, milk is secreted into the udder in preparation for the new born.

• At parturition, a yellowish coloured, salty liquid ‘Colostrum’ is secreted. This has very high

serum protein content and it provides antibodies to help protect the new born until its own

immune system is established.

The composition of colostrum changes to that of fresh milk within 72hours allowing it to be used in

food supply.

The Cow’s Milk-The essence of Milk Processing

In the cow, the period of lactation or milk production continues for an average of 305days,

producing 7000kg of milk.

It should be noted that a calf requires about 1000kg for growth. Hence, the need to process

the excess.

Within the lactation, the highest yield is 2-3months post-parturition, yielding 40-

50litres/day.

Within the milking lifetime; a cow reaches a peak in production about her third lactation, but

can be kept in production for 5-6 lactations if the yield is still good.

About 1-2 months after calving, the cow begins to come into heat again.

The cow is usually inseminated about 3 months after calving so as to come into a yearly

calving cycle.

Heifers are normally first inseminated at 15 months so that she is 2 years when the first calf

is born.

About 60 days before the next calving, the cow is dried off (there is no milking during this

stage). Reasons for this are:

o Milk has tapered off because of internal needs of the foetus.

o Udder needs time to prepare for the next milking cycle.


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Table 2: The cycle often repeated for 5-6 lactations

Age Event

0 Calf is born

15 months Heifer is inseminated for first calf

24 months First calf is born – starts milking

27 months Inseminated for second calf

34 months Dried off

36 months Second calf is born –starts milking

Milk Biosynthesis/Composition

Milk is synthesized in the mammary gland. Within the mammary gland is the milk producing

unit, ‘the alveolus.’

It contains a single layer of epithelial secretory cells surrounding a central storage area called

the ‘lumen’, which is connected to a duct system.

The secretory cells are, in turn, surrounded by a layer of myoepithelial cells and blood

capillaries.

The raw materials for milk production are transported via the blood stream to the secretory

cells. It takes 400 to 800 litres of blood to deliver components for 1 litre of milk. The

components are:

Proteins: The building blocks are amino acids in the blood. Casein micelles begin aggregation

in golgi vesicles within the secretory cells.

Lipids: C4-C14 fatty acids are synthesized in the cells.

Lactose: This regulates the volume of milk secreted by controlling the osmotic equilibrium of milk

with the blood.


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Udder showing mammary tissues

Biosynthesis of Milk

The components of milk are synthesized within the cells mainly by the endoplasmic

reticulum (ER) attached to ribosomes.

The energy for the ER is supplied by the mitochondria.

The components are then passed along to the golgi apparatus, which is responsible for their

eventual movement out of the cell in the form of vesicles.

Both vesicles containing aqueous non-fat components as well as liquid droplets (synthesized

by the ER) must pass through the cytoplasm and the apical plasma membrane to be

deposited in the lumen.

Milking stimuli such as a suckling calf, a warm wash cloth, the regime of milk parlour, vaginal-

tactile stimuation, the sight of the milking machine, etc., causes the release of a hormone called

‘oxytocin’ from the pituitary gland below the brain, to begin the process of milk ‘let-down’.

As a result of oxytocin stimulation, the muscles begin to compress the alveoli, causing a

pressure in the udder known as ‘letdown reflex’ and the milk components stored in the

lumen are released into the duct system.

The milk is forced down into the ‘teat cistern’ from which it is milked.

The let-down reflex fades as oxytocin is degraded, within 4-7min.

o Below is a flow diagram depicting the influence of milking stimulus


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Milking & Milking Methods

Lactation – the continuous secretion and storage of milk in the udder. The milk ejection or ‘let-

down’ reflex effect is short term, inhibited by pain or fear but stimulated by good husbandry

practices.

At least 10% of secreted milk is retained in the udder as residual milk.

Removal of milk is achieved when external forces such as suckling or milking open the teat

duct at the teat end.

Milk Secretion: is continuous & usually at a constant rate for at least 12 hours resulting in a gradual

increase in internal udder pressure. The ejection of milk is a neuro-hormonal reflex initiated by

various stimuli at milking time. Note: the stages of milk production are:

1. Cytologic and enzymatic differentiation

2. Copious secretion of mil

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